Internal combustion engines may include water injection systems that inject water from a storage tank into a plurality of locations, including an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Injecting water into the engine intake air may increase fuel economy and engine performance, as well as decrease engine emissions. When water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water. This heat transfer leads to evaporation, which results in cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. As mentioned above, water may be stored in a vehicle to provide water for injection on demand. However, in order to meet the water injection demands of an engine, a vehicle needs to have a sufficient supply of water. In one example, a water storage tank of a water injection may be manually refilled by a vehicle operator. However, in some situations, water for refilling the tank may not be readily available and having to re-fill the tank may be undesirable for the operator.
Other approaches to refilling a water storage tank includes collecting water (or condensate) from other vehicle systems on-board the vehicle, such as collecting water from exhaust gas flowing in an exhaust gas recirculation (EGR) system. Although exhaust gas has a high percentage of entrained water vapor relative to other vehicle systems, additional coolers and separators may be needed to effectively extract water from exhaust gas. For example, the approach shown by Piper and Windsor in U.S. Pat. No. 9,145,850 includes extracting water from a second EGR system cooler and separator arranged in line with a first cooler in an EGR system. However, the inventors have recognized potential issues with such methods. In particular, directing all exhaust flow from the engine cylinders through both the first and second cooler may result in accumulation of condensate beyond the capacity of a water storage tank and/or beyond a demanded water injection amount. Further, exhaust gas flow from the second cooler may be colder than desired for the intake passage and result in condensate formation at a compressor in a low-pressure EGR system.
In one example, the issues described above may be addressed by a method including extracting condensate from exhaust gases flowing through a second cooler, the second cooler arranged downstream of a first cooler in a passage disposed between and exhaust and intake of an engine, and storing the extracted, injecting the extracted condensate at an intake manifold, and adjusting one or more of an amount of the exhaust gas flowing through the second cooler and an amount of coolant flow through the second cooler based on an amount of stored extracted condensate. In this way, exhaust gas flow may be directed through the second cooler in response to an amount of stored condensate, thereby decreasing the likelihood of overfilling a water storage tank where the extracted condensate is stored. Additionally, when water extraction is not needed for refilling the water storage tank, exhaust gas flow may instead be directed through only the first cooler, thereby increasing engine efficiency and reducing a temperature of the exhaust gases entering the intake. Furthermore, in one example, flowing exhaust gases through the second cooler may include selectively directing the flow of exhaust gases from the second cooler to each of the intake upstream of a compressor and the intake downstream of the compressor based on a first operating condition. For example, exhaust gases may be directed to either upstream or downstream of the compressor based on one or more engine operating conditions and a temperature of the exhaust gases exiting the second cooler. As a result, compressor degradation may be reduce and a desired temperature of exhaust gases may be provided to the engine.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.